1. Field of the Invention
The present invention relates to a copper-based alloy with high conductivity, which is suitable for use in semiconductor lead frames, automobile radiator fins, and the like.
2. Description of the Related Art
Oxygen-free copper, phosphorous deoxidized copper, and an alloy of copper with 1% by weight of tin, which are widely known conventionally, have superior electrical conductivity and heat radiation properties. However, if these materials are heated to 250.degree. C. to 380.degree. C., they tend to soften so that during the assembly of semiconductor devices, the solder coating treatment of radiators, and similar processes, softening and heat distortion occur easily. Also, the materials have a tensile strength as low as about 40 kg/mm.sup.2. Accordingly, there are severe limitations in the manufacture of such materials, and, in addition, it is not possible to obtain satisfactory performance at time of use.
Lead frames for use in power transistors, in which a flowing electrical current reaches several amperes, require a conductivity in excess of 85% IACS as well as good heat radiation properties. Further, when assembling semiconductor devices at a temperature from 300.degree. C. to 450.degree. C., it requires the heat resistance so that heat distortion and softening are avoided. It is also necessary that the mechanical strength be such that it is difficult to produce abnormal deformation when shipping and assembling semiconductor parts. Also, because of continuing efforts to reduce the size of equipment, there is, in recent years, a trend toward thinner and thinner thicknesses and better heat radiation for fins used on automobile radiators. Accordingly, there is a need for the development of a material with a high mechanical strength to avoid the occurrence of breakage and deformation caused by handling of the material.